PORTSMOUTH, N.H. — Fourteen slaves who petitioned the New Hampshire Legislature for their freedom during the Revolutionary War were granted posthumous emancipation Friday when the governor signed a largely symbolic bill that supporters hope will encourage future generations to pursue social justice.

A group of 20 slaves who had fought in the war submitted a petition to the New Hampshire General Assembly on Nov. 12, 1779, while the war was still being fought. They argued that the freedom being sought by colonists should be extended to them, as well, and maintained that “public tyranny and slavery are alike detestable to minds conscious of the equal dignity of human nature.”...